package main

import "fmt"

func main()  {
	var num = 10
	fmt.Println(calzhishu(num))
}

func calzhishu(n int) int {
	count := 0
	m := map[int]bool{}
	for i:=2;i<n;i++ {
		v,exist := m[i]
		if !exist || !v {
			count++
		}
		for j := 2*i; j<n;j+=i  {
			m[j]=true
		}
	}
	return count
}
